11.4 Air Conditioning & Cabin Pressurisation - 14Q Flashcards
Name the sources of pneumatic air supply for air-conditioning
Primary bleed air = Engines
Secondary bleed air = APU, pneumatic ground cart
What area’s of an engine is air tapped from for supplying pneumatics to air-conditioning
Bleed air from the engines normally supplies the air conditioning systems
What is the most economical pneumatic source on the ground?
External air conditioning sources are more economical
What is the purpose of an emergency ram air system?
The system can be used in flight to ventilate the cockpit and cabin if all packs fail
or
for smoke removal only
(If ram air is used in flight, pressure differential must be no greater than 1 psi)
When using a pneumatic ground car to supply the air-con packs, you must ensure what?
Ensure that the air conditioning pack sources (APU,engines) are not also suppling air.
Air conditioning packs and external air conditioning sources should not supply an aircraft simultaneously to prevent excessive cabin airflow and possible air conditioning duct damage.
What can feed the Pack 1 air conditioning system?
(Isolation valve closed)
Engine 1
APU
Pneumatic ground cart
What can feed air conditioning PACK 2 ?
(Isolation valve closed)
Engine 2 only
What can the ground conditioned air connector do?
Ground conditioned air connected can feed air directly into the cabin, bypasssing all pack systems
If the ram air pushbutton is actuated, the _______ open to discharge the cabin pressure and the _________ opens to allow a ram air flow through the cockpit and cabin
outflow valve
ram air door
The ram air pushbutton should not be actuated before the cabin/ambient differential pressure is below _______ to prevent a rapid decompression of the cabin
1 psi
(c)
(b)
(c) Evaporator
Evaporator takes the absorbs the heat from the aircraft cabin into the refrigerant which causes it to evaporate.
Condensor condenses the hot refrigerant gas coming from the compressor. This is where the heat in the refrigerant is given up to the outside ambient temperature
Evaporator absorbs heat from cabin, condensor absorbs heat from refrigerant
(c) The turbine
(b) The structural stength of the aircraft cabin
(b) Cabin is not pressurised
(b) the outflow valve must be closed
(a) To regulate the cabin pressure
What is the purpose of an air-conditioning system?
(3 variables that should be controlled)
The purpose of the air conditioning system is to control temperature, the air flow and humidity within the aircraft cabin.
What temperature range is the aircraft cabin maintained to?
21 - 27 degrees
What is the purpose of trim air valves?
How many trim air valves are on an aircraft?
The trim air valves add an adjustable quantity of hot trim air from the engine to the cooled conditioned air from the mixer unit/ pack output
Each zone/pack will have a trim air valve and so the number of trim air valves depends on the number of zones
List the components of a vapour cycle system in order.
(also discription)
- Compressor - Increases temperature and pressure to make system more efficient
- Condensor - Refrigerant heat given up to outside ambient temperature
- Receiver Dryer - Dessicant that absorbs any moisture in the system
- Thermostatic / thermal expansion valve - regulates the amount of refrigerant liquid flowing into the evaporator
- Evaporator - Hot air taken from the cabin and transferred into the refrigerant
Explain the operation of the Vapour Cycle System
The vapor cycle system is an older air conditioning system that used refrigerant as medium to cool aircraft. It was used on older aircraft to cool cockpit and cabin.
The evarporator takes hot air from the cabin and transfers it to the refrigerant, evaporating it in the process.
It then flows to the compressor which heats it further and increases its temperature.
Hot and high pressure refrigerant then flows through the condensor where the heat is transferred to the outside ambient air. Refrigerant condenses.
Then flows through the Reciever Dryer which uses a dessicant to absorb any moisture
Then flows through the thermostatic/thermal expansion valve which only allows a certain amount of refrigerant into the evaporator.
List the components of an air-cycle system? (discription)
Compressor - increases heat and pressure of bleed air
Heat exchanger - heat in air transferred to ambient air
Turbine - takes energy from air cooling it further, uses this energy to drive compressor and cooling fan
Water separator - Absorbs the moisture from the air and re-uses it to make ambient air even colder by injecting it into stream
Pack anti -ice valve - can remove ice using warm air
Turbine bypass valve - controls output temperature along with RAM air inlet door
Flow control valve
How is heat removed in the ACM turbine?
The turbine takes energy from the air, with which the compressor and cooling fan are driven.
Removing energy from the air removes heat from it
'’Removing energy (cooling) atoms and molecules decreases their motion, resulting in a decrease in temperature’’
Heat exchanger also removes heat, but all to a lesser degree than the turbine
How is water removed from the conditioned air?
Water separator - separates, collects and removes excess moisture from the air before it enters the cabin.
It then uses this water to further cool Ram air increasing efficiency
What is the purpose of a pack valve?
Pack valve = Flow Control valve
The Pack valve/ Flow control valve allows a certain amount of bleed air from the engine through to the pack system and as trim air
I.e If one pack system fails, the flow control valve feeding that pack will need to be closed.
What is the purpose of recirculation fans and what percentage of the air is recirculated?
Recirculates air that is already in the cabin which reduces the workload of the packs
30-55% of the air in the cabin is recirculated
Is the isolation valve normally open or closed in normal flight?
The isolation valve is normally closed in flight
What do ‘exit louvers’ do?
Exit louvers allow air to get into the cargo compartment
What controls the Ram air doors?
The RAM air inlet door is controlled in conjunction (opposite control ie one open when one closed) with the turbine bypass valve to control output temperature of pack
Under what condition would you expect the turbine bypass valve to operate?
The turbine bypass valve is used to control the pack outlet temperature.
I would expect it to open if output temperature from the pack is too cold.
As it works in conjunction with RAM air inlet door, I would expect this door to close reducing the amount of cooling air taking heat from the bleed air again to help increase temperature.
What is the purpose of the re-circulation fan?
The purpose of the re-circulation fan is to recirculate air already in the cabin to reduce the work load on the packs.
Recirculated air = 30 - 55 % of cabin air
Humidity control can be divided into 2 parts. What are they?
Water Separator - removes moisture from cabin air
Water injector - injects water from water separator, combines it with trim air (hot air from engine) and injects it into ram air duct resulting in more heat being removed in the heat exchanger.
How is temperature controlled in the cabin?
Through a ‘Pack’
Older aircraft - Vapor Cycle System (Refrigerant)
Newer aircraft - Air cooling system (RAM air)
in an Air cooling System, The temperature in the cabin is controlled by varying the turbine bypass valve in conjunction with the RAM air inlet door.
What is the purpose of a mix valve?
Used on older aircraft
Mixes cold air and hot air upstream of pack
What is charge air?
Charge air is engine air
Bleed air from the engine
What is RAM air?
Air used to cool the pack
(outside air)
What is a Boot Strap System?
Boot Strap System = pack system (Air cycle cooling system)
How is the conditioned air distributed into the cabin and cargo bays?
Exit louvers
What equipment needs cooling?
Avionics Equipment
Where does ‘‘Gasper Air come from?
The individual air distribution system (Gasper) routes air from a pack to individually regulated outlets in the control & passenger cabins.
Adjustable nozle for each person provides supplemental cold air.
What is another name for the pack valve?
Flow control valve
What is the location of a trim air valve?
Downstream of the packs
What is the function of the Air Cycle Machine (ACM)
Turbine - converts heat energy to kinetic energy used to drive compressor and cooling fan, also cooling the air in the process
Compressor - compresses air increasing it’s temperature and pressure
Cooling fan - sucks in air at low airspeeds or on ground
Overall, the ACM’s job is to improve the efficiency of the system
What are the components of an air cycle machine?
- Turbine (converts heat energy to kinetic energy driving compressor and further decreasing temperature of output air)
- Compressor (compresses air increasing it’s temperature and pressure increasing efficiency)
- Cooling fan (draws in ram air at low speeds)
Where does the pack anti-ice valve prevent icing? (2 places)
- At the exit of the Air Cycle Machine (ACM) - Temperatures at the outlet of the turbine can theoretically drop to below 0 degrees
- Downstream of the water seperator
What kind of a switch is the switch for a pack valve?
(how controlled, how operated)
Electrically controlled, pneumatically operated
Variable switch for pack valve (flow control valve), can be low,norm or high
What component absorbs heat from the aircraft cabin in the vapor cycle system?
Evaporator - Evaporates refrigerant (Tetrafluorethane /R134A/ R12)
What’s the purpose of the thermostatic expansion valve in the vapor cycle system?
Regulates the amount of liquid refrigerant (Tetrafluorethane/ R134A / R12) flowing into the evaporator
What is the purpose of the blowout panels on an aircraft?
Blow-out panels are fitted in the floor between passenger and cargo compartments in order to prevent excessive differences in pressure occuring between these areas
What component controls cabin pressure?
The Outflow valve(s)
What component prevents cabin altitude from becoming higher than aircraft altitude?
Negative Relief (pressure) valve
Also known as vacuum relief valve
What position is the outflow valve in during and after landing?
Fully open
To equalise pressure inside and outside cabin
Also, so aircraft doesn’t have to withstand pressurisation and landing load during landing
What component sends signals to outflow valves?
2 electrical motors
AC motor for automatic mode - cabin pressure controller
DC motor for manual control - switch in cockpit
How does the negative relief valve protect the structure?
Equalises a possible negative pressure difference during descent
I.e outside air pressure increases faster than the pressure in the cabin
Allows greater pressure outside cabin inside cabin to equalise pressure and avoid structural damage
What’s the limit of the cabin altitude during pressurisation
(VSI) cabin altitude climb rate - 500 ft/min max
Cabin altitude cruise - 8,000 ft max
(VSI) cabin altitude descent rate - 300 ft/min max
What are the pressurisation indications in the cockpit ? (3)
- Cabin altitude Vertical Speed indicator (VSI) - (500ft/min ascent, 300ft/min descent)
- Cabin Differential altitude indicator
- Cabin altitude indicator (8,000ft max)
(Also position of outflow valves)
What is the refrigerant used in the Vapor Cycle System?
Tetrafluorethane / R134A / R12
(It cannot be mixed and must be drained at each top up)
Another name for the Pack valve is the?
Flow control valve
Trim air is taken _____ of the pack and deliverd ____ of the pack
Upstream
Downstream
As per CS-25, the Flow through the cabin while flying should be _______ Per Occupant
The cabin should be ketp to a temperature of ___ ^ and to a cabin pressure of ____ psi
1.2 Ib/min
25 degrees (21 - 27)
10.91 psi (8,000ft) cabin pressure
What precentage of cabin air is recirculated ?
30 - 55%
What should the temperature range inside the cabin be? (CS-25)
21 - 27 degrees
What are the 3 parameters that should be controlled in an aircraft environment?
Pressure (Outflow Valves)
Humidity (Pack System)
Temperature (Pack system)
What is the refrigerant used in the Vapor Cycle System?
The Refrigerant used is TFE
Tetrafluorethane / R134A / R12
What is the purpose of the Dessicant in the Reciever Dryer in the Vapor Cycle System?
The dessicant absorbs moisture from the refrigerant
What is the purpose of the Turbine in the Air Cycle Cooling System?
Converts heat energy to kinetic energy which is used to drive compressor and cooling fan as they are on the same shaft.
This conversion also decreases the temperature of the air further
Explain what happens at the water injector in an Air Cycle Cooling System?
Slightly warmer air mixes with cold water and causes it to vaporise
It is then injected into the RAM air stream making it even colder and more able to cool warm bypass air thus improving efficiency
(also gets rid of water content from water seperator)
Trim air valves add ___ ____ to the zones
hot air
Recirculation fans are used to take the load off the packs and the percentage of recirculated air is
30 - 55 %
The _____ _____ supplies cool air to individual seats
Gasper System
Fow what purpose are flow limiter or fuses used in a brake system?
Flow Iimiters and fuses in a brake system keep all the brakes from becoming pressureless if one of the brakes or brake lines leaks. They shut off further hydraulic supply to the particular brake, so that the complete hydraulic system is not drained.
Explain how the parking brake works?
This means constant hydraulic pressure on
the brake cylinders. It is done by pressing the pedals completely down and then locking them with the help of the Parking Brake Lever. lf the hydraulic power system is switched off, a hydraulic accumulator supplies pressure to the brake cylinders.
